I was told that you need a letter from your consultant/GP stating that you are fit to fly and to take a couple of copies of the letter as you will need one for the return journey if they keep the original.
Luckily my arm is now ok so I don't need one for when I fly to Greece tomorrow.
(See general chat thread on Greek Islands forum)

Moved to flights.

Mark

You may find that she will need a new cast, made looser to make way for swelling up on the plane or in the heat.

Yes, you'll need a letter as explained by Grecophile and you'll have to let your travel insurance company know.

Depending on which bone and how bad the fracture is, sometimes the hospital will either make a split in the plaster cast or apply what is called a back slab, which is half a plaster bandaged into place...this accommodates any swelling that occurs during the flight.

Sanjiiiiiiiiiiiii

Knowing XL's routes, you SHOULD be OK - but I believe it is still the case that some countries insist that you carry a copy of your X-rays to prove the fracture exists - I understand this is possibly a customs requirement to stop the unscrupulous using the cast to smuggle illicit items. Your travel agent should be able to research this for you to check that no similar restrictions exist for your destination.

And make sure your travel insurers are made aware BEFORE you travel!

most charter airlines are fine with a cast as long as it is at least 24hrs old, that is fine for most people as you are unlikely to have a cast put on the day before you fly, unless you are v v unlucky!!